The present invention concerns a device for heaving in and paying out chains using one or more hydraulic cylinders which, by means of gripping and locking devices, grip the chain and lift or lower it a little while the locking device is disengaged. When the cylinder approaches the other end of its stroke, the locking device is re-engaged, the gripping device is released from the chain and, after the hydraulic cylinder has returned to its initial position, the gripping device is ready to grip again.
Several such types of linear winches for chains exist. They usually consist of three separate units:
A locking device for chains.
A cylinder device connected to a gripping device for the chain. The cylinder device can lift or lower the chain a little more than two chain links.
A 180xc2x0 guide device for the chain which is raised/lowered vertically back to a parallel vertical direction towards a box or similar for storing the chain.
The locking device and gripping device are often arranged according to the same principle: one or two pawls which engage with every other chain link using the force of gravity, springs or similar. When the chain is lifted, the as pawl(s) move aside, but the pawl(s) will fall back in place when the chain is lifted two chain links.
Such devices only work for heaving in the chain. If the chain is to be paid out, the pawls in the locking device and gripping device must be operated separately, for example by means of hydraulic auxiliary cylinders
Jacking devices having two parallel cylinders can give problems regarding the synchronisation thereof, while a device having one cylinder can cause high bending moments on the piston rod. Cylinders where the working pressure acts on the rod side of the piston (the piston rod is pulling) provide reduced power as compared to cylinders where the working pressure acts on the entire piston (the piston rod is pushing).
U.S. Pat. No. 3,845,935 shows a device where the piston rod is stationary and the gripping device is attached to the cylinder. Since the chain force causes a high bending moment in the piston rod, the latter is very robust. For the cylinder there are provided two bearing supports arranged at a considerable distance from the piston rod, which increases the total length substantially. The patent does not show any 180xc2x0 guide device for the chain, but this will be necessary if the device is to be used for anchor chains.
In U.S. Pat. No. 4,183,502 the bending moment in the piston rod has been avoided by placing the working cylinder centrally between two chains. This will not function properly for two anchor chains which often will have substantially different loads. The locking and gripping device is rot pawls, but two parallel bolts pushed in on either side of a chain link in order to lock the link above.
U.S. Pat. No. 5,909,869 shows a semi-circular guide device for the chain. The guide device is pivotal about a pin near the periphery, and about diagonally thereof an upper pawl is arranged which can lock the chain to the periphery of the guide device, the pawl being supported in the structure of the guide device. A frame supports the pivot pin, a lower chain stopper and a support for a pushing cylinder. The piston rod with its head is supported in the guide device. When the cylinder pivots the guide device, the chain is lifted out of the lower chain stopper until it can hold the chain two links below. When the cylinder pivots the guide device back to its starting position, the chain will slide on the guide device and the upper pawl will grip the chain two links below.
The present invention, as defined in claim 1, has some similarities to the patent mentioned above. The frame has the same functions: supporting the guide device, holding the lower chain stopper, and supporting the pushing cylinder.
However, there are substantial differences which in many instances can be advantageous: the guide device is a rotatable chain wheel having pockets for the chain, and the pawl co-operates with the pockets and constitutes the upper chain stopper. The pawl is supported in two brackets, one on either side, and the two brackets are supported for rotation about the axis of the chain wheel. The pivot pin which provides support for the pawl in the brackets, may also form the support for the head on the piston rod of the pushing cylinder, although the support for the head may instead be a third pivot pin arranged in the two brackets. The two brackets may possibly be interconnected through a suitable structure.
The U.S. Pat. No. 5,909,869 mentioned above has advantages as compared to the other patents discussed above, i.a. as regards space requirements since it has moderate dimensions. The dimensions of the winch according to the present invention may be reduced even further. The diameter of the guide device (the chain wheel) is reduced to less than half. The chain force, which is held by the lower chain stopper when the winch is not in operation, will be transmitted to the upper chain stopper in periods during the operation. The force exerted by the upper chain stopper is transmitted through the two supports in the frame. In an advantageous embodiment according to the invention, the two supports are located at about the same distance from the chain on either side. Consequently, the chain force is held by about one half by each of the two supports in the frame, and the forces may simply be transmitted further to the area of the lower chain stopper. The structure may thereby be made compact where the large loads occur.